Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0006—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format
  • H04L1/0007—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format by modifying the frame length
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
  • H04B7/2659—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA] for data rate control
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
  • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
  • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes

Definitions

• the present invention relates to communications methods and systems (apparatus), and more particularly to methods and systems for allocating resources in wireless communications.
• Wireless communications systems are commonly employed to provide voice and/or data communications to subscriber stations.
• analog cellular radiotelephone systems such as those designated AMPS, ETACS, NMT-450, and NMT-900, have long been deployed successfully throughout the world.
• Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990's.
• PCS Personal Communications Services
• DECT Digital Enhanced Cordless Telephone
• CDPD Cellular Digital Packet Data
• FIG 1 illustrates a typical terrestrial cellular radiotelephone communication system 20.
• the cellular radiotelephone system 20 may include one or more subscriber stations such as radiotelephones 22, communicating with a plurality of cells 24 served by base stations 26 and a Mobile Telephone Switching Office (MTSO) 28.
• MTSO Mobile Telephone Switching Office
• a typical cellular network may include hundreds of cells, may include more than one MTSO, and may serve thousands of radiotelephones.
• the cells 24 generally serve as nodes in the communication system 20, from which links are established between radiotelephones 22 and the MTSO 28, by way of the base stations 26 serving the cells 24.
• Each cell 24 will have allocated to it one or more dedicated control channels and one or more traffic channels.
• a control channel is a dedicated channel used for transmitting cell identification and paging information.
• the traffic channels carry the voice and/or data information.
• a duplex radio communication link may be established between two radiotelephones 22 or between a radiotelephone 22 and a landline telephone user 32 through a Public Switched Telephone Network (PSTN) 34.
• PSTN Public Switched Telephone Network
• the function of a base station 26 is to handle radio communication between a cell 24 and radiotelephones 22. In this capacity, a base station 26 functions as a relay station for data and voice signals.
• a satellite 42 may be employed to perform similar functions to those performed by a conventional terrestrial base station, for example, to serve areas in which population is sparsely distributed or which have rugged topography that tends to make conventional landline telephone or terrestrial cellular telephone infrastructure technically or economically impractical.
• a satellite radiotelephone system 40 typically includes one or more satellites 42 that serve as relays or transponders between one or more earth stations 44 and subscriber stations such as satellite radiotelephones 23.
• the satellite conveys radiotelephone communications over duplex links 46 to satellite radiotelephones 23 and an earth station 44.
• the earth station 44 may in turn be coimected to a PSTN 34, allowing communications between satellite radiotelephones, and communications between satellite radiotelephones and conventional terrestrial cellular radiotelephones or landline telephones.
• the satellite radiotelephone system 40 may utilize a single antenna beam covering the entire area served by the system, or, as shown, the satellite may be designed such that it produces multiple minimally-overlapping beams 48, each serving distinct geographical coverage areas 50 in the system's service region.
• the coverage areas 50 serve a similar function to the cells 24 of the terrestrial cellular system 20 of Figure 1.
• FDMA Frequency Division Multiple Access
• AMPS advanced mobile phone service
• TDMA Time Division Multiple Access
• TLA Telecommunication Industry Association
• EIA Electronic Industries Association
• DAMPS digital AMPS
• GSM global system for mobile communication
• CDMA Code Division Multiple Access
• Traditional analog cellular systems generally use FDMA to create communications channels.
• Radiotelephone communications signals are generally modulated waveforms that are communicated over predetermined frequency bands in a spectrum of carrier frequencies.
• each of these discrete frequency bands may serve as a channel over which cellular radiotelephones communicate with a base station or satellite serving a cell.
• the available frequency spectrum may need to be managed with greater efficiency to provide more channels while maintaining communications quality. This challenge may be further complicated because subscriber stations may not be uniformly distributed among cells in the system. More channels may be needed for particular cells to handle potentially higher local subscriber station densities at any given time. For example, a cell in an urban area might contain hundreds or thousands of subscriber stations at certain times, which may exhaust the number of channels available in the cell.
• frequency bands may be allocated to each cell such that cells using the same frequencies are geographically separated to allow subscriber stations in different cells to use the same frequency simultaneously without interfering with each other. Accordingly, for example, many thousands of subscriber stations may be served by a system having only several hundred allocated frequency bands.
• a TDMA system may be implemented by subdividing the frequency bands used in conventional FDMA systems into sequential time slots. Communication over a frequency band typically occurs via a repetitive TDMA frame structure wherein each frame includes a plurality of time slots, also referred to herein as sub-periods. Each subscriber station communicates with the base station using bursts of digital data transmitted during the subscriber station's assigned time slots.
• a channel in a TDMA system may include at least one time slot on at least one frequency band, and typically includes at least one time slot in each of a plurality of frames.
• channels may be used to communicate voice, data, and/or other information between users, e.g., between a subscriber station and a wireline telephone.
• CDMA systems such as those conforming to the IS-95 standard, can achieve increased channel capacity by using "spread spectrum” techniques wherein a channel is defined by modulating a data-modulated carrier signal by a unique spreading code, i.e., a code that spreads an original data-modulated carrier over a wide portion of the frequency spectrum in which the communications system operates.
• a unique spreading code i.e., a code that spreads an original data-modulated carrier over a wide portion of the frequency spectrum in which the communications system operates.
• the subscriber stations may include traditional radiotelephones or mobile terminals. These devices may include a serial data port in which a device, such as a computer or Personal Digital Assistant (PDA), may be connected to establish a wireless data connection.
• PDA Personal Digital Assistant
• the subscriber stations also may include such wireless communications devices which are being used for voice calls, data calls, facsimile transfer, Internet access, paging, and other personal organization features such as calendar management or even travel directions via the Global Positioning System (GPS).
• GPS Global Positioning System
• These devices may include a cellular radiotelephone with a multi-line display, a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities, a PDA that can include a radiotelephone, pager, Internet intranet access, Web browser, organizer, calendar and/or a GPS receiver, and conventional laptop and/or palmtop receivers that include radiotelephone transceivers.
• PCS Personal Communications System
• Embodiments of the present invention wirelessly transmit data from a base station, and/or wirelessly receive data at a plurality of subscriber stations that are at a plurality of distances from the base station using a Time Division Multiple Access (TDMA) frame by transmitting a same amount of data to each of the subscriber stations at a same power level during the TDMA frame while varying at least one other parameter as a function of the distance of the respective subscriber station from the base station.
• TDMA Time Division Multiple Access
• the at least one other parameter may be an amount of error correction coding, a sub-period duration in the TDMA frame, a number of modulation symbols from a set of modulation symbols and/or a number of sub-periods of the TDMA frame.
• Figure 1 is a schematic diagram illustrating a conventional terrestrial cellular communications system.
• Figure 2 is a schematic diagram illustrating a conventional satellite -based wireless communications system.
• Figure 3 is a schematic diagram illustrating an exemplary wireless communications system according to embodiments of the present invention.
• Figure 4 is a schematic diagram illustrating an exemplary subscriber station according to embodiments of the present invention.
• Figure 5 graphically illustrates overlapping CDMA signals of graduated power levels pursuant to U.S. Patent 5,345,598.
• Figure 6 is a flowchart of operations for transmitting data according to embodiments of the present invention.
• Figure 7 is a flowchart of operations for receiving data according to embodiments of the present invention.
• Figure 8 is a flowchart of operations for transmitting data according to other embodiments of the present invention.
• Figure 9 is a flowchart of operations for receiving data according to other embodiments of the present invention.
• Figure 10 graphically illustrates time division multiplexing of data packets of different duration and/or coding according to embodiments of the invention.
• Figure 11 graphically illustrates signal-to-interference ratio (C/I) versus distance (R) from a base station to a cell center.
• the wireless communications system 300 includes a base station 320 and a resource allocator 312.
• the base station 320 includes an antenna 326, a TDMA transceiver 324, and a controller 322 that controls the operations of the transceiver 324.
• the base station 320 may include many other components, such as power supplies and other support equipment, and that the TDMA transceiver 324 may include various combinations of components such as mixers, demodulators, decoders, timing generators, and a variety of other communications components. The detailed operations of such components are known to those skilled in the art, and a detailed description thereof is not necessary to understanding of the present invention.
• the resource allocator 312 is illustrated as implemented in a mobile switching center 310 coupled to the base station 320.
• the resource allocator 312 is operative to assign time slots, spreading codes, coding rates, and bandwidth to subscriber stations communicating with the base station 320 according to various aspects of the present invention described in greater detail herein.
• resource allocator 312 is here illustrated as implemented in the MSC 310, functions of the resource allocator 312 may be implemented in other communications system components, such as in the base station 320 and may, in general, be distributed among commonly-used components of a wireless communications system infrastructure. It will also be appreciated that the resource allocator 312 may be implemented using special-purpose hardware, software and/or firmware executing on special or general purpose computing system, or combinations thereof.
• FIG. 4 illustrates a subscriber station 400 in which systems and methods according to the present invention may be embodied.
• the subscriber station 400 includes an antenna 410 for transmitting and receiving Radio Frequency (RF) signals.
• the subscriber station 400 also includes a user interface 412 including a display 420, a keypad 430, a speaker 440 and/or a microphone 450.
• the subscriber station 400 further includes a controller 470 that controls the operations of the user interface 412, and a TDMA transceiver 480 that is coupled to the antenna 410 and is controlled by the controller 470.
• the controller 470 is also operatively associated with a memory 460 of the subscriber station 400 that stores, for example, program instructions and data used by the controller 470.
• the TDMA transceiver 480 may include various combinations of components such as mixers, demodulators, decoders, timing generators, and a variety of other communications components.
• the controller 470 may include, for example, a microprocessor, microcontroller and/or other data processing device that is operative to load and execute computer instructions for performing functions described herein. It also will be understood that the functionality of the transceiver 480, the controller 470 and/or the memory 460 may be combined. It is known to use varying power levels of sub-periods of a TDMA frame for various reasons. See, for example, U.S. Patent No. 6,072,792 to Mazur et al.
• CDMA signals at different power levels See, for example, U.S. Patent No. 5,345,598 to the present inventor Dent entitled Duplex Power Control System in a Communications Network, the disclosure of which is hereby incorporated herein by reference in its entirety.
• Figure 5 graphically illustrates overlapping CDMA signals of graduated power level pursuant to U.S. Patent 5,345,598.
• Embodiments of the present invention wirelessly transmit data from a base station, and wirelessly receive data at a plurality of subscriber stations that are at a plurality of distances from the base station using a Time Division Multiple Access (TDMA) frame by transmitting a same amount of data to each of the subscriber stations at a same power level during the TDMA frame while varying at least one other parameter as a function of the distance of the respective subscriber station from the base station.
• TDMA Time Division Multiple Access
• the term "function of distance” shall include a function of propagation path loss as well.
• the at least one other parameter may be at least one of an amount of error correction coding, a sub-period duration in the TDMA frame, a number of modulation symbols from a set of modulation symbols and a number of sub-periods of the TDMA frame.
• the function of distance may be a linear or nonlinear, monotonic or nonmonotonic, continuous or discontinuous function of distance.
• base stations transmit a radio signal of a given signal spectral bandwidth due to modulation with a coded symbol stream.
• the coded symbol stream for each base station is formed by time- multiplexing coded symbol streams to be transmitted to subscriber stations it is currently serving, and which lie at different distances from the base station, to form a time-division-multiplex frame with a frame repetition period.
• Data symbols for a subscriber station lying close to the base station and therefore receiving a strong signal with high signal-to-interference ratio may be coded into multi-level modulation symbols with little additional error-correction coding redundancy and therefore can occupy a small fraction of the TDMA frame period.
• data symbols intended for a subscriber station at a larger distance from the base station and closer to a neighboring interfering station may be coded into modulation symbols having a fewer number of levels and/or may use a greater amount of error correction coding redundancy, thereby using a greater number of modulation symbols to convey the same amount of data and therefore occupying a greater proportion of the TDMA frame period.
• embodiments of the invention allocate a different proportion of the TDMA transmission period to convey the same quantum of data, a data packet, to different subscriber stations as a function of their distance from the base station or more specifically according to the signal-to-noise-plus-interference ratio they are experiencing at their individual locations.
• all the coded modulation symbols for one subscriber station are transmitted in a clump followed by all the coded modulation symbols for the next subscriber, and so forth.
• Each subscriber station in these embodiments need only capture and decode in every TDMA frame period only the clump of coded modulation symbols assigned to the subscriber station.
• differently coded symbols for different subscriber stations may be interleaved while leaving the number of symbols per frame and the frame period unchanged as compared with the embodiments described in the immediately preceding paragraph.
• a given subscriber station may demodulate and/or decode symbols other than its own intended symbols in order to assist in demodulating and/or decoding its own intended symbols.
• a subscriber station lying at an intermediate distance from a base station may easily decode more heavily coded symbols intended for a more distant station and may use the decoded result to help with estimating the fading properties of the multipath propagation and/or with equalizing the received signal for multipath distortion.
• a same amount of data may be obtained for each subscriber station.
• the same amount to data may be a same amount of bits to be transmitted. It also will be understood that the bits can represent digital data, audio, video, graphics and/or multimedia information.
• at Block 620 at least one parameter is varied as a function of the distance of the respective subscriber station. It will be understood that the function need not be varied in direct proportion to the distance as long as the parameter is varied as some function of distance of the respective subscriber station.
• the same amount of data is transmitted to each subscriber station at the same power level during a TDMA frame.
• the operations return to Block 610. If not, then the operations end.
• the amount of error correction coding of the same amount of data to each of the subscriber stations is varied.
• the TDMA frame comprises a plurality of sub-periods of varying duration and the sub-period duration is varied as a function, such as a fourth power function, of the distance of the respective subscriber station from the base station.
• the sub-period duration and the amount of error correction coding both are varied.
• the data is modulated based on a number of modulation symbols from a set of a modulation symbols and the number of modulation symbols from the set of modulation symbols is varied as a function, such as a power function, of the distance of the respective subscriber station from the base station.
• the number of modulation symbols and the amount of error correction coding of the data is varied as a function, such as a power function, of the distance of the respective subscriber station from the base station.
• the TDMA frame comprises a plurality of sub-periods of same duration and the number of sub-periods is varied as a function, such as a power function, of the distance of the respective subscriber station from the base station.
• the number of sub-periods and the amount of error correction coding is varied. Additional discussion of each of these embodiments will be provided below.
• TDMA transceiver 480 and/or controller 470 of Figure 4 operations to receive data according to embodiments of the invention are described. These operations may be carried out by the TDMA transceiver 480 and/or controller 470 of Figure 4.
• a portion of a TDMA frame is received at a power level that is independent of the location of the subscriber station relative to the base station, but including at least one other parameter that varies as a function of the location of the subscriber station relative to the base station.
• the portion of the TDMA frame is decoded to obtain an amount of data that is independent of the location of the subscriber station. If additional frames are received at Block 730, the operations at Block 710 repeat. If not, operations end.
• the parameter variation of Block 710 may include those that were described above in connection with Block 620, and need not be described again herein.
• TDMA frame and appropriate sub-periods are defined.
• data is coded for multiple subscriber stations in a manner that depends on the distance or path loss to the subscriber station from the base station.
• the TDMA frame is transmitted to the subscriber stations.
• operations at Block 810 are repeated. If not, operations end. It will be understood that these operations may be performed by the resource allocator 312, controller 322 and/or TDMA transceiver 324 of Figure 3.
• the multiplexed time period is divided into sub-periods of graduated duration.
• data for transmission to a nearer subscriber station is coded to occupy a sub-period of shortest duration.
• Data for transmission to a furthest subscriber station is coded to occupy a sub-period of longest duration.
• Data for transmission to subscriber stations lying at intermediate distances is coded to occupy sub-periods of duration between the longest and the shortest sub-period of duration.
• the multiplexed time period including the coded data is wirelessly transmitted to the plurality of subscriber stations at Block 830.
• a time division multiplexed frame period is defined in which a number M of modulation signals are transmitted, at Block 810.
• data is coded for transmission to a nearest subscriber station, to occupy a smallest subset Ml of the M modulation symbols.
• Data for transmission to a furthest subscriber station is coded to occupy a largest subset M2 of the M modulation symbols.
• Data for transmission to subscriber stations lying at intermediate distances is coded to occupy subsets of the M modulation symbols containing a number of symbols intermediate between the smallest and the largest subsets of the symbols.
• the time division multiplex frame including the coded data is wirelessly transmitted to the plurality of subscriber stations. .
• a time division multiplex frame period is divided into a number M of time slots, in each of which a number L of modulation symbols are transmitted.
• data is coded for transmission to a nearest subscriber station to occupy a smallest subset Ml of the M time slots.
• Data for transmission to a furthest subscriber station is coded to occupy a largest subset M2 of the M time slots.
• Data is coded for transmission to subscriber stations lying at intermediate distances to occupy subsets of the M time slots containing a number of time slots intermediate between the smallest and the largest subsets of slots.
• the time division multiplex frame period including the coded data is wirelessly transmitted to the plurality of subscriber stations.
• FIG. 9 operations for receiving data that is transmitted according to embodiments of Figure 8 now will be described. These operations may be performed by the TDMA transceiver 480 and/or controller 470 of Figure 4. As shown at Block 910, at least portion of a TDMA frame is received. At Block 920, the data is decoded as a function of the distance of the subscriber terminal from the base station. Decoding may be performed using a decoding scheme which is complementary to the appropriate coding scheme of Block 820. If additional frames are present at Block 930, the operations of Block 910 are performed again. If not, operations end.
• Figure 10 graphically illustrates time-division multiplexing of data packets of different duration and/or coding according to embodiments of the invention.
• Packets intended for closer subscriber stations are transmitted at the same power level as packets intended for more distant subscriber stations, but occupy a shorter time duration and therefore consume proportionally less energy from the transmitter, as energy is equal to power times time.
• an expectation was that reducing the power transmitted to nearer subscriber stations would allow more subscriber stations to be accommodated within the transmitter power budget and interference budget. However, this expectation may only be partly fulfilled.
• reducing the time duration of transmissions to closer subscriber stations can allow more subscriber stations to be accommodated within a given TDMA frame repetition period. This potential advantage need not be reduced by own-cell interference, as different signals
• Figure 11 graphically illustrates signal-to-interference ratio (C/I) versus distance (R) from a base station at the cell center.
• C/I signal-to-interference ratio
• R distance
• Figure 11 graphically illustrates signal-to-interference ratio (C/I) versus distance (R) from a base station at the cell center.
• the spread of values at the cell edge represents different angular positions in the cell. Angular position may be irrelevant to the C/I when the subscriber station is closer to the cell center, however. It may be seen from Figure 1 1 that the C/I experienced by a subscriber station, with all other cells in the system transmitting on the same frequency at the same power level, varies from about -ldB at the cell edge to over 40dB at less than l/8th cell radius from the center.
• embodiments of the invention ideally can allocate less than 1/10000th of the time for transmitting to a subscriber station at radius less than R/8 compared to the time allocated to transmit to a subscriber station at radius R, a subscriber station at radius R/4 about 1/lOOOth of the time, a subscriber station at R/2 about 1/50th of the time, and so forth, where the sum of the times over all subscriber stations is equal to a frame repetition period.
• Another factor that may be taken into account is the geographic distribution of subscriber stations. With a uniform area distribution, the number of subscriber stations at a given radius increases in proportion to the area of a ring at that radius, which increases proportionally to radius.
• the number of subscriber stations situated in the vicinity of R 8 is one eighth of the number of subscriber stations situated near cell edge.
• the percentage of the frame period to assign the correct proportion of transmitter energy to each subscriber station is shown, and may be compared with 6.67% (1/16th) that would be assigned if all subscriber stations received an equal proportion. From this, the increase in capacity or per-subscriber station data rate using embodiments of the invention may be determined. Instead of receiving 6.67% of the frame period, the subscriber station at rl6 receives 21.32%, over three times as much. Thus the subscriber station is able to receive three times as much data per frame period than with an equal distribution of frame time to the subscriber stations.
• a practical design of such a system may assign frame time to subscriber stations in discrete quanta or time slots using a discontinuous function of distance.
• a TDMA system can also be constructed in which the total number of symbols in a frame period is divided in roughly the above-tabulated percentages between different subscriber stations.
• One exemplary system could comprise dividing the frame period into 32 slots each containing 120 data symbols plus other fixed symbols such as syncwords to assist demodulation and equalization for multipath propagation.
• the total of 3840 data symbols may be divided between a number of subscriber stations in the proportions shown in Table 2. Two subscriber stations are sacrificed because of the quantization.
• data is encoded and modulated such that each subscriber station decodes the same amount of data, substantially error free.
• the C/I is 17dB and at this value a high order signal constellation such as 16-PSK or 16QAM may be used, conveying four bits per symbol.
• 96 bits are transmitted including error correction coding.
• a minimum of error correction coding may be used, for example a rate 5/6ths code, which results in decoding 80 information bits from the 96 bits.
• Codes of the exact desired coding rates such as 80/(4 x 39), for r5 may be produced by starting with a rational code such as rate l/3rd, and puncturing it to delete bits from the decoder output until the desired number of transmitted symbols is obtained.
• Such a code can, for example, comprise transmitting five repeats of each symbol, which when combined raise the C/I by 7dB to 4-5.5dB, and using a rate 400/818 or approximately rate 1/2 code.
• symbols assigned to a particular subscriber station need not be sequentially transmitted. Rather, symbols may be interleaved in a predetermined fashion to provide time-diversity and some potential benefit in fading situations, which may be determined by simulation as is well known to one skilled in the art. Therefore the choice of interleaving or no interleaving may be based on particular applications and fading situations, which may depend on radio frequency band, speed of mobile subscriber stations, propagation path and terrain, etc.
• the present inventor has pointed out in U.S. Patent Application Serial No. 09/066,669 filed April 28, 1998 and entitled "Transmitter/Receiver for GMSK and Offset-QAM", the disclosure of which is hereby incorporated herein by reference, that the lower order constellation can be defined as containing a subset of the constellation points of the higher order constellation such that both may be transmitted using the same transmitter by feeding in an appropriate modulation bit pattern. Both also may be received using the same subscriber station by constraining the subscriber station to detect only symbols within the applicable subset of constellation points.
• 14 subscriber stations can each receive the same 80 decoded bits per frame. If the frame had by contrast been divided into 14 equal time slots each conveying approximately 274 symbols, and the same coding rate of approximately 1/10 had been used as for rl6 as above in order to operate at his -1.5dB C/I, then the data rate would have been only 27 bits per frame instead of 80, illustrating a potential factor of three improvement.
• codes may be designed for perhaps 90% packet success rate, and to employ acknowledgment and automatic request for retransmission (ARQ). In that way, the average data rate may be increased further.
• every subscriber station need not receive exactly the same data rate all the time. Subscriber stations in favorable situations can be offered higher data rates so as to complete data transfers with reduced delay, so that they can vacate the channel earlier and the capacity released can be offered to another subscriber station, thereby allowing capacity to increase.
• 32 time slots can be divided between 11 subscriber stations as shown in Table 3:
• each of the above 1 1 subscriber stations can decode 120 data bits per TDMA frame period substantially error free.
• the number of slot repeats for each adapts the performance to their respective C/I ratios. Subscriber stations in more favorable positions may reduce the coding rate to receive higher data rates.
• Mobile data systems also may be characterized by a very dynamic demand, where a subscriber station requests data at a random time, is queued for service, receives the data, and then the channel is allocated to the next subscriber station in the queue.
• a subscriber station requests data at a random time, is queued for service, receives the data, and then the channel is allocated to the next subscriber station in the queue.
• the division of a frame period into various numbers of symbols or slots destined for different subscriber stations may change from frame to frame.
• a subscriber station may attempt to decode all data to determine if it is addressed to the subscriber station, and discard that which is not.
• the frame can use specific symbols at the beginning, coded heavily enough so that all subscriber stations at all ranges can decode them, to indicate what fraction of the frame is allocated to each subscriber station.
• This may be simplified if there are only a finite number of ways, numbered 1 to 16 for example, in which the frame symbols can be divided between subscriber stations, each with a predetermined code and/or interleaving pattern. Then, a four-bit number linked to each subscriber station address may be transmitted to indicate the division it will receive in this frame or a subsequent frame.
• the network may determine the division that the subscriber station will receive based, for example, on a C/I report that the subscriber station transmits with a request for data or acknowledgment of previously received data.
• the network may maintain a separate queue for requests that could be fulfilled by each of the exemplary 16 ways of dividing the frame.
• a request could be fulfilled either when a free space became available at the head of the respective queue or a lower C/I queue, so that each request may be fulfilled in the most timely fashion and with at least adequate coding.
• the principles outlined above may be adapted by one skilled in the art to design systems and methods that fulfill requests for varying data rates by allocating different proportions of the transmitted frame time to different subscriber stations as a function of the requested rate and the subscriber station's C/I.
• Multiple radio frequency channels may also be operated from the same transmitting station, and requests may be fulfilled by assigning both a channel frequency and a division of the frame symbols to a subscriber station in a channel assignment message such as disclosed above.

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